Free cutting alloys



Patented Jan. 7, 1936 FREE CUTTING ALLOYS Louis Kemp! and Walter'A. Dean, Cleveland, I Ohio, assignors to Aluminum Company of America, Pittsburgh Pennsylvania 4 Pa., a corporation of No Drawing. Original application September 18,

1933, Serial No. 689,886. Divided and this application May 3, 1935, Serial No. 19,626

3 Claims.

The invention relates to aluminum base alloys and is particularly concerned with alloys of this nature containing substantial amounts of copper.

This application is a division of our copending application Serial No. 689,886, filed September 18, 1933. Alloys disclosed but not claimed herein are claimed in our copending application Serial No.

19,627, filed May 3, 1935. 4

Despite the manifold advantages connected with the use of aluminum and its alloys in commercial fields, there is an inherent drawback which somewhat curtails their use in certain p tential adaptations. Aluminum alloys, for instance, containing from about4 per cent to about 12 per cent of copper have a wide range of usefulness because of their favorable mechanical properties and their susceptibility to improvement by suitable thermal treatments. Mechanical cutting operations, howe er, such as boring, drilling, planing, or lathe-cutting are successfully carried out only by usingcertain precautions which increase the expense of the operation and which occasionally necessitate the substitution of another alloy which may be machined more readily but which is otherwise not so desirable from the standpoint of physical properties. When alloys are diflicult to machine this disadvantage bedomes evident in many cases through rapid wear of the cutting tool edge whichnecessitates frequent resharpening. In such cases where ma- .ehining is diiiicult, continual lubrication is required. The machined surface is rough and irregular, and the chip has a tendency to form continuous curls or spirals that may foul the tool or the operating parts of the-machine. These drawbacks retard production and increase the cost of operation. Many articles require a variety of machining operations before being applied to their final purpose and it is particularly desirable that these articles be'finished economically andsatisfactorily;

An object of this invention, therefore, is the production of alloys containing substantial amounts of copper which may be readily machined. 1 j

A further object is the production of such alloys whose mechanical properties in the preferred composition range are perfectly adequate to suit most commercial purposes, 7

These objects we have effected by the addition to, aluminum-copper-tin alloys of at least one of the elements lead, bismuth or For-,the plnposes of our invention these elements are substantially equivalent, their behaviorin alloys of the class herein described being similar in their effect on machining characteristics.

' We have discovered that tin, when used in amount between about 0.01 per cent and 2 per cent in aluminum base alloys containing from about 4 per cent to about 12 per cent of copper, forms a particularly desirable base alloy to which can be added one or more of the alloying elements lead, bismuth or thallium. The lead may be present in amount between about 0.1 per cent and per cent, the bismuth between about 0.05 per cent and 1.5 per cent, and the thallium between about 0.05 per cent and 3 per cent. These elements, in combination with tin in aluminum-copper alloys, have a very favorable eifect on the machining properties of the alloys. In this sense the elements tin, lead, bismuth and thallium may be termed free machining constituents, just as the alloys they form are now called free. machining" alloys, to indicate the fact that they may be machined more rapidly, with better quality of chip, and cleaner machined surface than similar alloys not containing the tin, bismuth,- lead or thallium.

Tin within the disclosed range effects an increase in the tensile strength, shear strength, and 25 Brinell hardness of the aluminumcopper alloys,

while the elongation is caused to drop off correspondingly. The remaining constituents, namely lead, bismuth, or thallium, appear not to materially aifect, in many cases, the mechanical properties of the aluminum-copper alloys except insofar asthey are beneficial to the machining properties. We have found that when the tin is used in combination with one or more of the other free machining elements lead, bismuth or thallium, the advantageous effect of the tin on the tensile strength, shear strength and hardness of the aluminum-copper alloys is not diminished mate-' rially, whereas the machining properties of the resulting alloys are very materially accentuated. 40 The simultaneous presence of more than one of the free machining elements is more advantageous than that of the same total amount of either of the elements used separately. If, for instance, we are working with an aluminum base alloy containing about 6.0 per cent of cop'perand 1.0 percent of tin,.and in a particular application we desire to add. about 1.5 percent of free machining constituents in combination with the tin, it is more advantageous to make up this 1.5V per cent by using more than one of the elements lead, bismuth or thallium, than to add 1.5 per cent of one element alone. In conformity with the same principle the addition of one or. more of the I elements lead, bismuth or thallium to the alumificial efiect in cutting characteristics of the alloys.

If onlyone of the elements lead, bismuth or thallium is to be added to aluminum-copper-tin alloys, we prefer to use about 1.0 per cent of the element. As a preferred alloy base we use an aluminumalloy containing about6 per cent of copper and 0.1 per cent of tin. If more than one of the elements lead, bismuth or thallium is to be added to an aluminum-copper-tin alloy, the preferred amount of free machining elements, inclusive of the tin, should also be about 1.0 per cent, although amounts in excess of this composition, and up to the total amount of each disclosed hereinbefore, continue to exert a beneficial effect on the cutting properties of the alloy. The preferred amount of 1.0 per cent of total free machining constituents represents a point at which the mechanical properties and the machining properties of the alloy reach a'most favorable balance, although, of course, there may be many commercial applications wherein improved machining characteristics may more than compensate for the lowering of the mechanical proper-- ties.

The tin, lead, bismuth and thallium may be added by introducing th'ese constituents in solid form into a molten heat of the aluminum-copper alloy, since they melt at a temperature considerably below that customarily encountered in the commercial handling of molten aluminum or its alloys in the foundry. Since the specific gravity of the disclosed free machining elements is considerably higher than that of aluminum and their liquid solubility is limited, the melt should be heated somewhat above the ordinary temperature and stirred vigorously to assure a thorough mixture of the alloying constituents. The method of adding heavy low melting point metals to aluminum here referred to is more fully described in copending application, Serial No. 689,885 now issued as U. S. Patent No. 1,959,029. 10

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those skilled in the art of treating aluminum-copper alloys for the purpose of altering their physical characteristics. 15

The term aluminum as used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade or picked up in the course of the usual handling operations incident to ordinary melting practice. 20

We claim:

1. An aluminum base alloy containing from about 4 per cent to about 12 per cent of copper. from about 0.01 to 2 per cent of tin and from about 0.05 to 1.5 per cent of bismuth, the balance 25 being aluminum.

2. An aluminum base alloy containing from about 4 to about 12 per cent of copper, from about 0.01 to 2 per cent of tin and about 1 per cent 01' bismuth, the balance being aluminum. 30

3. An aluminum base alloy containing about 6 per cent of copper, about 0.1- per cent of tin, about 1 per cent of bismuth, the balance being aluminum.

LOUIS W. KEMPF. 35 WALTER A. DEAN. 

